This paper reports an investigation of air-jet texturing of technical polyester yarns without causing important decrease in their breaking strength. The overfeed levels are kept low in order to maintain the parallel fiber alignment which is essential to maintain the yarn strength. Surface of the fibers are analyzed by scanning electron microscopy (SEM) studies. Results show rougher surfaces after air-jet texturing. Optical microscopy is used to study the yarn structure. An increased overfeed level results in more loops on the surface. Furthermore, flexural rigidity of the fibers is calculated and it is concluded that fibers with high flexural rigidities give open loop structure, whereas the fibers with low flexural rigidities result in closed loops.